In general, a CCFL is used to serve the panel of a liquid crystal display (LCD). The ground level can be caused to fluctuate at the moment when the CCFL is lighted. When the fluctuation of the ground level is further synchronized with a synchronizing signal, the voltage of the LCD can be caused to be unstable, so that the ripple-stripe phenomenon easily appears.
The synchronizing signal is a control signal and is also a trigger signal. It may be a pulse signal and may also be either a sine wave or an irregular pulse signal. A control signal is referred to the synchronizing signal as long as it can make the frequency or the phase of the controlled device reach a coincidence and can make the controlled device change with the predetermined schedule.
In the prior art, a method avoiding the ripple-stripe phenomenon is that the lighting frequency of the CCFL is synchronized with the frequency of the synchronizing signal of the LCD. Although this processing method using the illusion of the vision solves the ripple-stripe problem, yet another problem is derived therefrom; i.e.; in internal processing, the synchronizing signal of some of LCD control integrated circuits can delay a pulse. FIG. 1(a) shows a conventional synchronizing signal used to drive a driving integrated circuit of a CCFL of an LCDTV. The display frequency of the picture fields of the LCDTV is 60 Hz (or 50 Hz), and the lighting frequency of the CCFL is 48.5 KHz, wherein the lighting frequency is controlled by the frequency of the synchronizing signal VSYN. As one period being a reciprocal of the frequency 60 Hz (or 50 Hz) cannot just accommodate complete cycles of pulses having the frequency 48.5 KHz, the synchronizing signal of some of the LCD control integrated circuits can delay a pulse.
Please refer to FIG. 1(b), which is a schematic diagram showing conventional waveforms including a synchronizing signal VSYNC of an LCD and a lamp current ICCFL, corresponding to the synchronizing signal VSYNC, of a CCFL. As shown, when a pulse of the synchronizing signal VSYNC is lost due to delay, a pulse, corresponding to the lost pulse, of the lighting signal of the CCFL also disappear. Therefore, both the lamp voltage and the lamp current ICCFL of the CCFL are lowered, which makes the ripple-stripe or the picture-field flicker phenomenon.
How to solve the picture-field flicker phenomenon, caused due to a pulse delayed in the synchronizing signal, by an effective and brief circuit becomes the primary motive of the present invention.